1. Technical Field
The present invention relates generally to electronic media storage and retrieval and in particular to an improved method and apparatus for locating and tracking robotic units in a storage system.
2. Description of Related Art
Automated data storage library systems provide a means for large quantities of information to be efficiently stored and retrieved by external systems. These systems generally include one or more robotic units that move data storage media to and from read/write devices where the information can be accessed. In order to control these movements, the precise location of the robotic mechanisms within the library relative to the data storage media and the read/write devices must be known. An example of such a system is a tape library. In this case, tape cartridges are stored in specific locations within a structure, and a robotic unit moves about the structure, transferring cartridges to and from tape drives where the information can be accessed by an external host.
Such systems often rely on optical encoders mounted on the robot drive motors to provide the library control unit with position information via an electrical cable. In this case, the robot's position is known relative to a fixed position, typically a mechanical stop that the robot is driven to during an initialization cycle. The position of the robot is then known based on the number of encoder tach counts from the fixed initialization position. Although this method of positioning the robot has been proven to be sufficient and reliable, it does have its issues. If the control system fails or loses control of the robotics for any reason, the position of the robot will become unknown. This means that the robot must be driven to the fixed initialization position and then the entire library must be audited. Also, optical encoders necessary for this type of positioning scheme add cost to the library. Each motor that drives the robot must have an encoder. Several motors can be necessary depending on the complexity of the library and robot geometry. Finally, mechanical tolerances inherent in this system contribute to position errors.
Therefore, it would be advantageous to have an improved method and apparatus for identifying the position of robots in an automated data storage library.